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Home , Brachycercus, Brachycercus harrisella, Caenidae, Ephemera (mayfly), Ephemera danica, Ephemeridae

A SCOPING STUDY ON

THE EPHEMEROPTERA

OF SOUTHERN CHALK

STREAMS

A Report to the Envinulinent Agency

.1 F Wright .1 II Blackburn 121 NI Gunn K I. Symes •1 Bowker

Institute of htshuater Ecology Laboratory East Stoke W.NI2E11.1N1 121120 611B

A pril 1998 =I IM 61•1•11111•1=10110110111100 MEN Scoping Study on the Ephemeroptera of Southern Chalk

J F Wright, J H Blackburn, R J IVIGunn, K L Symes & J Bowker

Research contractor: Institute of Freshwater Ecology

Environment Agency House Sunrise Business Park Higher Road DTI 1 8ST Publishing Organisation Environment Agency Rivers House Sunrise Business Park Higher Shaftesbury Road Blandford Forum DT11 8ST

Tel 01258 456080 Fax: 01258 455998

C) Environment Agency 1998

All rights reserved. No part of this document may be produced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of the Environment Agency.

The views expressed in this document are not necessarily those of the Environment Agency. Its officers servant or agents accept no liability whatsoever for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained herein.

Dissemination Status Internal: Released to South-West, Southern, Thames and Anglian Region. External: Restricted

Statement of Use This short scientific review was commissioned to further a 'LEAP' action to investigate factors which potentially could contribute to an alleged decline in Ephemeroptera within the Avon catchment. The review has relevance to other chalk systems within the UK and should significantly contribute to the Agency's knowledge, enabling future monitoring to be focused on specific aspects which influence this group.

Research Contractor This document was produced under the Technical Services Agreement by:

Institute of Freshwater Ecology River Laboratory East Stoke Wareham BH20 6BB

Tel: 01929 462314 Fax. 01929 462180

Environment Agency Project Manager Mr A. Frake, Environment Agency, South West Region. ACKNOWLEDGEMENTS

The authors would like to thank the Environment Agency, South West Region for initiating this study. In particular, we thank Dr. G.P.Green and Dr. D.A.Cooling for helpful discussions at the outset and Mr. A Frake for his advice as Nominated Officer to the project. Funding for the report was provided under the Technical Services Agreement between the Environment Agency and the Institute of Freshwater Ecology.

INTELLECTUAL PROPERTY RIGHTS

CONFIDENTIALITY STATEMENT

'In accordance with our normal practice, this report is for the use only of the party to whom it is addressed, and no responsibility is accepted to any third party for the whole or any part of its contentg Neither the whole nor any part of this report or any reference thereto may be included in any published document, circular or statement, nor published or referred to in any way without our written approval of the form and context in which it may appear.' WIIMMIIINIMUNIIMMIIMMIMMININIMOINIII0

CONTENTS Page

Acknowledgmen ts

List of Tables

List of Figures

List of Appendices

Executive Summary vii

Key Words viii

I. Introduction 1.1 Background to the Study 1 1.2 The British Ephemeroptera () 1

2. The Ephemeroptera of southern chalk streams 3 2.1 characteristic of southern chalk streams 3 2.2 Seasonal occurrence of larvae 5 2.3 Species richness at chalk sites 6 2.4 Longitudinal occurrence of species 8 2.5 Abundance of families at sites 9

3. Notes on the life cycles of each species 13

4. Factors affecting the distribution and abundance of Ephemeroptera 17 4.1 Habitats, habits and feeding behaviour of the larvae 17 4.2 The impact of regime 19 4.3 The impact of pollution 21 4.4 Factors affecting the terrestrial (adult) phase 23

5. References 25

Appendices 29 1•11-1•11•11MOIIININIIIIIIIMIN•11•1111•10 a IIMINI LIST OF TABLES Page

21 Listing of the mayflies recorded at 42 chalk stream sites, together with 4 I the numbcr of sites at which each taxon was found. Data from RIVPACS samples (three seasons samples combined)

I 2.2 Frequency of occurrence of larvae in 42 chalk stream sites 6 by season

I 2.3 Longitudinal occurrence of mayfly larvae at 42 chalk stream sites 9

3.1 Information on the flight periods and life cycles of mayflies abstracted 14 I from Elliott & Humpesch (1983) and Elliott eta (1988), together with additional observations made on southcrn chalk streams

1 4 1 Running-water habitats (from Wright et al. 1993), together with 17 habits and feeding behaviour (from Elliott c/at 1988) for the I mayflies found in southern chalk streams

I LIST OF FIGURES

2 I Number of species of mayfly larvae recorded at 42 chalk stream sites 7

22 Mayfly species richness for 42 chalk stream sites in relation to location 7 downstream

2.3 Log. category abundance data for each mayfly family at 42 chalk stream I 1 sites in , summer and autumn.

LIST OF APPENDICES

I Appendix 1. Specification for the scoping study 29

Appendix 2. The 42 southern chalk stream sites for which RIVPACS samples 30 I have been obtained.

Appendix 3. Mayflies found at each of the 42 chalk stream sites Data for the 31 1 three seasons are combined (1 indicates taxon occurrence in a single season, whereas 2 (or 3) indicates presence in two (or 3) seasons.

I

1 MINIMIINIIIMMINIIIIIMMINIIIIIIMISM EXECUTIVE SUMMARY

This scoping study was undertaken at the request of the Environment Agency, following expressions of concern from fishermen that some species of Ephemeroptera (mayflies) appear to have declined on the R.Wylye and on the upper reaches of the Hampshire Avon. The purpose of this scoping study is to provide a short scientific review of the mayfly fauna of southern chalk streams.

• Forty nine species of mayflies are known to occur in Britain. The status of two additional species is uncertain. An appraisal of the R1VPACS III data-base yielded 42 high quality sites on southern chalk streams. Examination of the species lists for these sites confirmed that over 50% of the British species occur on southern chalk streams. Information is provided on the seasonal occurrence of the different species and their frequency of occurrence at the 42 sites.

Between four and fifteen species of mayflies were recorded per site, with an arithmetic mean of 9.12 per site. The most species-rich sites (12 or more species) occurred between 10 and 50, km from stream source. They included sites on such well known rivers as the R. Frome (Dorset), R. lichen, R. Lambourn, Moors River (Dorset) and R.Test. The study includes information on the longitudinal occurrence of each species.

The R1VPACS III data-set also includes information on the log, categories of abundance of each family of mayfly in spring, summer and autumn, based on the standard R1VPACS pond-net samples. This provides a useful general guide on whether a given family is scarcc, common or abundant in a given season. Members of the were found to be important components of the mayfly fauna in spring, summer and autumn, but were particularly abundant at most sites in summer. were also very abundant at most sites in summer.

Notes are provided on the flight period and life cycles of each species, as far as these are known The life cycles of some species show flexibility and some members of the Baetidae are capable of having several generations in a year. Hence, interpretation of the life cycle can pose problems

Information on the habitats, habits and feeding behaviour of the larvae demonstrates that a wide variety of different habitats and food resources are exploited by mayfly larvae.

A consideration of the potential impact of flow regime on larval populations suggests that if changes in the flow regime affect the habitats and food resources within a stream, then there are likely to be consequences for the mayfly fauna. However, different members of the mayfly fauna may respond in different ways, given their various adaptations.

Low flows arc of particular interest at present, and several short term studies on chalk streams, together with one long-term study on the R.Lambourn in the 1970's, are starting to provide scientific data on the way in which different components of the

VII mayfly fauna appear to respond to the discharge regime. Some provisional findings for the Baetidae, Ephemerellidae and are given below.

A nine-year study on the R. Lambourn provided evidence that in early June, densities of larvae in the Baetidae (which may have included up to six species) were low in drought years (-500 ni2) compared with some years with high discharge when densities were —5,000 1112.

Densities of larvae in the Ephemerellidae (Ephemerella ignita only) were higher in the year following a drought.

Densities of larvae in the Ephemeridae ( danica only) did not appear to be related to the prevailing discharge regime in the R. Lambourn. Instead, cool damp conditions during the period of flight activity in May/June of one year resulted in very low larval densities of the next generation in December of that year. Over the next three generations (at intervals of two years), larval densities increased progressively in the December following oviposition.

Studies commissioned by the Environment Agency on a number of chalk stream sites first examined in the 1970's may soon provide further information on the response of mayflies to the flow regime.

Some chalk streams may be subject to organic pollution as a result of , fish farm effluent or farm wastes. Low levels of organic enrichment may not have adverse effects on the mayfly fauna, but more severe cases of organic pollution will result in the progressive elimination of the more sensitive species. Environment Agency biologists are well-versed in the detection of organic pollution using standard methodologies.

Although the time spent in the aerial phase of the life cycle is only a small fraction of the total life span, it is crucial for successful reproduction and dispersal. Despite predation and parasites, the subimagos and imagos normally find suitable shelter and terrain markers for swarming, thereby ensuring that mating and subsequent oviposition is successful. However, as previously indicated for , there is circumstantial evidence that inclement weather is capable of disrupting this critical phase of the life cycle.

KEY WORDS

Chalk stream; Ephemeroptera; mayflies; distribution; low flows; pollution I. INTRODUCTION

1.1. Background to the study

The need for this scoping study was identified during a meeting between staff from the Environment Agency (EA) and the Institute of Freshwater Ecology (IFE) which took place at the River Laboratory in late August 1997. EA staff indicated that there had been expressions of concern from fishermen, alleging a decline in Ephemeroptera (mayflies) within some of the Hampshire Avon (R.Wylye & Upper Avon). In particular, concern focused on poor hatches of mayflies in the family Baetidae.

As a result of the initial meeting, the ME was asked to develop some proposals under three separate headings.

A short scientific review of the mayfly fauna of southern chalk streams.

An appraisal of a very limited data-set held by the WE on the mayfly larvae of one or two sites on the R Wylye and Upper Avon for the 1970's, to determine whether there was merit in repeating these surveys.

An outline proposal for the long-term monitoring of chalk stream mayflies, with particular regard to the emergent stage of the life cycle.

Following a consideration of these outline proposals from the IFE, the EA requested separate quotations for items a). and c). Funding for a short scientific review of the mayfly fauna of southern chalk streams (item a) was approved in November 1997 and forms the subject of the present report. The agreed specification for the review is given in Appendix 1.

1.2. The British Ephemeroptera (mayflies)

Worldwide, the order Ephemeroptera is quite small, with something in excess of 2,000 known species in approximately 200 genera and 19 families (Brittain, 1982). Until recently, the British list included 48 species in eighteen genera and just eight families (Elliott, Humpesch & Macan, 1988). However, two of the species on this list, Arthroplea congener Bengtsson and Heinagenia longicauda (Stephens), have not been recorded since the 1920's/1930's and may no longer occur in the British Isles (Bratton, 1990). Refer to Elliott, Humpesch & Macan (1988) for the checklist of 48 British species.

In the last few years, examination of specimens from many streams and rivers in Great Britain has revealed three additional species previously recognised on mainland Europe, but unknown in Britain. These are pseuclorivulonnn Kieffermuller (Gunn and Blackburn, 1997) and Cactus heskidensis Sowa (Gunn and Blackburn (in press)) in the family and Electrogena affinis (Eaton) (Blackburn, Gunn and Hammett (in press)) in the . Thus, at present, 49 species of mayflies are known to occur in Britain with two additional species of uncertain status • OM NM 01 INSIMINNOWINIMMINNEINIIIIMMINNIMI 2. THE EPHEMEROPTERA OF SOUTHERN CHALK STREAMS

2.1. Species characteristic of southern chalk streams

The RIVPACS III data-set, which includes species-level data for many chalk stream sites of high quality in southern England, was used to determine which species occurred in chalk streams. For the purposes of this scoping study, the EA nominated officer and IFE staff agreed that 'southern' chalk streams would be defined as occurring in three EA regions (Thames, Southern and South-West region) and that whereas the source waters would always be derived from chalk , sites would continue to be defined as chalk stream sites when the course of the river progressed over different geology (e.g. tertiary gravels). This protocol generated a total of 42 chalk stream sites which are listed in Appendix 2. In turn, these sites yielded 26 mayfly taxa (mainly species, but including two genera and two species 'groups') in six families. There were no records for two families ( and ).

A list of the mayflies which were characteristic of chalk stream sites, together with their frequency of occurrence at the 42 sites is given in Table 2.1. The Baetidae, represented by 12 taxa in four genera, was by far the most taxon-rich family in southern chalk streams. All taxa were identified to species with the exception of the Bactis scambus group, which comprised both B. scambus Eaton and B.fuscaffis (Linnaeus). These two species, which are difficult to separate as larvae, were always treated as a 'species group' in the RIVPACS project. Within the Baths, one species (B.digitatus), is known from a very limited number of sites in Britain (including non-chalk stream sites) but others, such as B.rhodani, B.vernus and B.scambus group occurred in a majority of the chalk stream sites and normally formed an important element of the fauna. Additional species, including B.muticus and B.niger were frequent and B. atrebatinus and B. buceratus were also encountered quite frequently. Of the remaining species in the Baetidae, Centroptilum luteolum occurred in over half of the chalk stream sites, but C. pennulatum, Procloeon bifidum and were less commonly encountered.

Members of the family Heptageniidae, are usually associated with fast-flowing upland streams, but one species, Ileptagenia sulphurea, is characteristic of chalk stream sites. Two other genera were also represented, but were infrequent in the data-set. They were Rhithrogena sp.(either R. germanica or R.semicolorata) and Ecdyonurus sp. (four species in this genus). Within the RIVPACS project, an early decision was made not to attempt to distinguish the larvae of the different species in these two genera due to inherent problems with small specimens Hence, the results are presented at generic level

The family , includes three genera and all were represented in the chalk stream data-set. However, vespertina, which is more characteristic of still waters, was recorded only once and fusca was only recorded at two sites. All three species in the genus were present and Paraleptophleffia suhmarginata was found at 20 of the 42 sites. In contrast, P.cincla

3 was only recorded twice and /' werneri, a rare species with Red Data Book 3 status (Bratton, 1990), which is most characteristic of winterbourne streams (intermittent chalk streams), was found at a single site.

The Ephemeridae includes three British species but only Ephemera danica, the fisherman's mayfly, was a common and characteristic species of southern chalk streams.

Table 2.1 Listing of the mayflies recorded at 42 chalk stream sites, together with the number of sites at which each taxon was found. Data from RIVPACS samples (three seasons samples combined)

Family S eciesNo. of Occurrences

Bactidac Baetis atrebatinus EatonI I &ens buceratus Eaton10 Baths chgatatus Bengtsson1 Baths muticus (L.)17 Baebs mger (L.)I 7 Bae rhodatu (Pictet)41 Baths vernus Curtis37 Baths scambus group'30 Centroptilutn luteolum (Muller)24 Centroptilurn pennulatum Eaton6 Cloeon dipterum (L.)2 Procloeon bifidum (Bengtsson)3

Heptagenlidae Rhathrogena sp 5 lieptagenta stdphurea (Muller) 24 Ecdyonurus sp. 4

Leptophlebiidae Leptophlebin vespertina (L ) Paraleptophlebta cmcta (Retzaus) 2 Paredeptophlebia submargtnata (Stephens) 20 Paraleptophlebta.werneri Ulmer 1 Habrophlebta fusca (Curtis) 2

Ephemeridac Ephemera dantca Muller 31

Ephcmcrellidae Ephemerella ignita (Poda) 42

Caenidac3 harrisella Curtis 2 (L.) 1 Cactus rivutorum Eaton 24 group2 25

Includes Baths scambus Eaton and &ens fuscams (Linnaeus)

2 Includes Caenis lucluosa (Burmeister) and Cactus macrura Stephens

3 Recently, Caems pusdla was identified amongst Caenids in samples from the Test, ltchen & Hants Avon. However, the data-base has not yet been updated.

4 The family Ephemerellidae includes two species, of which just one, Ephemerella ignita, known to fishermen as the blue-winged olive, was present at every site.

Finally, members of the Caenidae, often referred to as the Angler's Curse, were represented by four taxa. Two of them (Brachycercus harrtsella and Caenis horaria) were rarely recorded, being more characteristic of other types of flowing and standing waters. However, Caents rivulorum and the Caenis luctuosa group (which includes both C.luctuosa (Burmeister) and C. macrura Stephens, which are difficult to separate as larvae) were both encountered at more than half of the chalk stream sites in the data-set.

A full listing of the mayflies recorded at each of the 42 chalk stream sites is given in Appendix 3. This list combines the records for the three seasons (spring, summer and autumn) in which the RIVPACS samples were collected, such that 1 indicates that a given taxon occurred in a single season, whereas 2 (or 3) indicates presence in two (or 3) seasons

2.2. Seasonal occurrence of larvae

Each RIVPACS sample was collected by pond-net and involved sampling all available habitats in proportion to their occurrence over a period of 3 minutes in each of spring, summer and autumn. These seasons were broadly defined due to the scale of the sampling operation. They were spring (March - May), summer (June - August) and autumn (September - November).

The frequency of occurrence of each species by season is given in Table 2.2. The results provide a broad indication of the season or seasons in which the larvae of a given species may be found and whether they are common, frequent or rare in a chalk stream.

However, it would be unwise to over-interpret the information in the table without prior knowledge of the life cycles of the individual species (See Section 3 of this report). For example, both Baths rhodani and Ephemera danica occur at many sites in spring, summer and autumn, but whereas in chalk streams, B. rhodani appears to have several generations per year (multivoltinc), E.danica has one generation every two years (semivoltine). Again, B.muticus and B. niger overwinter as larvae and are most frequent in spring, whereas B.vernus and B.scambus group overwinter in the egg stage and are most frequent in summer.

In cases where there are few records for a species, it is even more important to be aware of the life cycle, because a single record in a given season may have very little or alternatively, considerable significance. An example of the latter is the single record of Paraleptophlebta werneri in spring. This species is characteristic of calcareous streams, and in particular winterbournes. When present in winterbournes, the larvae must complete their larval stage in spring and emerge before the stream dries up in summer. Resistant eggs in the then survive the period of drought through the autumn and early winter. Table 2.2 Frequency of occurrence of mayfly larvae in 42 chalk stream sites by season.

No. of Occurrences S ecics Sprin Summer Autumn

Thetis atrebatinus 4 6 6 Baetis buceratus 7 5 2 Baetis digitatus 0 1 0 Baetis muticus 15 11 5 Bactis niger 14 7 5 Bactis rhodani 35 33 34 Baetis vernus 14 33 27 Baetis scambus group 8 28 19 Centroptilum luteolum 13 13 11 Centroptilum pennulatum 0 5 3 Cloeon dipterum 0 1 1 Proclaeon bifidum 0 3 0

Rhithrogena sp. 5 2 2 Heptagenia sulphurea 21 12 18 Ecdyonurus sp. 1 3 2

Leptophlebia vespertino 1 0 0 Paraleptophlebia cincta 0 2 0 Parateptophlebia submarginata 10 3 17 Paraleptophlebia werneri 1 0 0 Hobrophlebia fusca 1 1 1

Ephemera danica 28 23 26

Ephemerella ignita 25 41 28

Brachycercus harrisella 0 2 0 Caenis horaria 0 0 1 Coenis rivulorum 18 5 9 Caenis luctuosa group 9 18 11

2.3. Species richness at chalk stream sites

The number of mayfly taxa recorded in the combined seasons RIVPACS samples at the 42 sites varied from 4 to 15 with an arithmetic mean of 9.12 taxa per site (Fig.2.1). These numbers should not be regarded as the full compliment of species occurring at each site, but probably give a reasonable indication of site richness. For example, the three 3-minute RIVPACS samples for the R.Lambourn at Bagnor yielded 12 species. A very comprehensive sampling programme undertaken throughout the 1970's yielded just two additional species.

In view of the variation in the number of species found at different sites, there is a necd to consider whether mayfly richness has a tendency to vary with location downstream

6 In •

7

6

S .

4

3 •

2

—t—t—tllt ui 1 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17I1h18 19 20 NumberofSpecies

Figure 2 I Number of species of mayfly larvae recorded at 42 chalk stream sites

Figure 2.2 presents site species richness in relation to distance downstream. It is apparent that sites with relatively low richness (say, six or fewer species) are most frequently encountered at locations less than 20km or over 75km from source.

18

16 Is 211 14 7• 40 i • 65 7. 2k.., 12 85 9* •• • t.g 10 • • se• a • • • • •••• 1 8 es • E • Z 6 es a • a • • 4 le 2

0 I i 1 1 1 I 1 I

0 10 20 30 40 50 60 70 80 90 100

Kin from source

I Moom/Crane at Romlbrd Bridge 6 lichen dis Chickenhall SDW 2 Frome at Moreton 7 Teal at Skidmore 3 lichen at lichen St Cross Larnhoum at l3agnor 4 Test at Lower Brook 9 lichen at Otterhourne Water Works 5 Prone at East Stoke

Figure 2.2 Mayfly species richness for 42 chalk stream sites in relation to location downstream.

7 In contrast, sites with twelve or more species only occurred between 10 and 50km from source. It is possible that some of the sites with just four or five species had experienced some form of natural or man-induced stress prior to sampling and may be capable of supporting more species. The most species rich sites have been labelled 1-9 and are identified in a footnote to Fig.2.2. They include a number of the most famous chalk streams in southern England (R. Frome in Dorset, R.Test, R.Itchen and R.Lambourn) and other rivers (R.Crane/Moors River) recognised for the high species richness of their macroinvertebrate assemblages (Wright et al.1988).

2.4. Longitudinal occurrence of species

In order to investigate the basis of this variation in site richness, it is necessary to examine the longitudinal occurrence of the individual species. In Table 2 3 the 42 sites have been placed into a series of eight categories representing distance from source. The distance categories are <5, <10, <15, <20, <30, <40, < 60 and <100km from source. The total number of sites in each distance category is given at the head of the table and this is followed by information on the longitudinal occurrence of each species

Within the Bactidae, Baths rhodani, B.vernus and also Centroptilum luteolum were common or frequent in all distance categories. Several other species, including B.muticus, B. niger and B. scambus group were also widely distributed, although less frequent at sites <10 km from source. Additional species in the genus Baths (B. atrebatinus, buceratus and digitalus) appeared most consistently in the middle and lower reaches of chalk streams, as did C. pennulatum, Cloeon dipterum and Procloeon bifidum.

In the Heptageniidac, whereas both Heptagenia sulphurea and Ecdyonurus p. were widely distributed, Rhithrogena sp. was never recorded more than 15 km from source.

Similarly, within the Leptophlebiidae there was evidence of spatial separation of species. is more characteristic of ponds, lakes and slow- flowing streams and hence the single record in the lower reaches of a chalk stream was to be not entirely unexpected. Whereas Paraleptophlebia submarginata is widespread in chalk streams, P.citwta, though occasionally recorded, is more frequent in other river systems. In contrast, P.werneri, which has R.DB3 status, is normally found in winterbournes and the upper perennial sections of chalk streams. Although the single R1VPACS site rccord was at 5.1 km from source on the R.Crane, the species was also recorded at a further site 3 5 km from source on the R. Crane which dried out in summer and was rejected as a R1VPACS site. Habrophlebia fusca is also most frequently encountered in small streams.

Both the Ephemeridae and Ephemerellidae were represented by single species (Ephemera danica and Ephemerella ignita respectively), which were widely distributed along the length of southern chalk streams

Finally, the four taxa within the Caenidae included two species (Brachycentrus harrisella and Caenis horaria) typical of silty rivers which were restricted to downstream locations and two others (C. rivulorum and C. luctiosa group) which were more widespread in their occurrence.

Table 2.3 Longitudinal occurrence of mayfly larvae at 42 chalk stream sites

Distancefrom Source (km) <5 <10 <15 <20 <30 <40 <60 <100 Number of sites in cute or 6 5 8 5 5 5 4 4

3 I Baetis atrebatinus - I 2 4 4 Baths buceratus I I I 1 2 - - Baetis digttatus - 1 Baetis muticus 1 2 3 1 1 5 4 - Baetis mger 1 I 5 1 3 4 2 Baetis rhodani 6 5 8 5 5 5 4 3 3 3 Baetis vernus 5 5 8 4 5 4 &Jetts scambus group I I 5 5 5 5 4 4 Centroptilum luteolum 2 3 7 3 3 3 2 2 Centroptilum pennulaturn - I 2 2 1 1 Cloeon dipterum - 1 1 _ Procloeon hifidurn - 1 I Rhithrogena sp. I 2 2 3 1 Heptagenia sulphurea 2 2 5 2 4 5 Ecdyonurus sp. I I I I Leptophlebia vespertina - 1 1 Paraleptophlebia cincta 1 1 I Paraleptophlebia submarginata 2 3 3 2 3 5 Paraleptophlebia werneri I - Habrophlebia fusca I I Ephemera danica 4 3 7 4 4 3 4 2 Ephemerella ignita 6 5 8 5 5 5 4 4 I I Caenis horaria - 1 1 Caenis rivulorum 3 2 5 2 4 4 3 Caenis luctuosa group 2 I 3 5 4 3 3 4

2.5. Abundance of families at chalk stream sites

The species-level data for mayflies at all R1VPACS sites is simply presence/absence data with no indication of whether the individual species are abundant, common or scarce at each site. Each 3-minute R1VPACS sample was obtained by pond-netting all available habitats, with the time roughly allocated in proportion to the area of each habitat. The resulting sample was therefore effort-dependant, and whilst it was NOT a quantitative sample, it did include crude information on whether taxa were common or scarce. In view of the potential value of this information, it was decided to estimate the abundance of every family of macroinvertebrate in each sample in terms of log categories of abundance (i e 1=less than 10 individuals per sample; 2=<100, 3=<1,000; 4=

Baetidae were present at almost all sites in each of spring, summer and autumn. They were also a dominant element of the mayfly fauna in most seasons, particularly in summer when over 30 sites recorded log category 3 abundance (i.e. between 100 and 999 specimens per 3-minute sample).

The Heptageniidae were dominated by a single species, fleptagema sulphurea and summer emergence dictated that densities of larvae would be lowest at this time.

The Leptophlebiidae were also dominated by a single species (Paraleptophlebia submarginata) and once again, early summer emergence resulted in lower densities of larvae at this time before the next generation appeared in autumn.

Ephemera danica, the only species of Ephemeridae recorded at the 42 chalk stream sites, has a two year life cycle and therefore, apart from the emergence of some larvae in the second half of May resulting in lower abundances in summer, the changes in abundance were relatively damped.

Once again, the Ephemerellidae were represented by a single species, the ubiquitous Ephemerella ignita. Although this species was recorded at every site (Table 2.1), the life cycle resulted in most sites having their highest abundances of this important member of the mayfly fauna in summer.

Finally, the Caenidae, with four taxa included in the data-set (plus the recently recorded C.pusilla), appeared to be progressively less abundant from spring to autumn. The number of sites at which they occurred also decreased with season.

Standard RIVPACS samples, as collected and processed by the Environment Agency, frequently have log, abundance categories ascribed to each I3MWP family, including the six families of Ephemeroptera featured above. The information presented in Fig. 2.3 provides a record of the range of abundance categories observed over 42 different chalk stream sites in three seasons. Previously unsampled chalk stream sites which are examined in a given season could exhibit any of the results shown in the figure. However, at high quality sites, some results are more likely than others, and for example, there are very few chalk stream sites in Fig. 2.3 in which the Baetidae are not abundant in summer. Hence, used with caution, this Figure may offer some early clues on whether newly sampled sites are poorly represented in terms of their mayfly larvae Note, however, that the use of full R1V1ACS predictions at the family abundance level will provide more detailed predictions tailored to the specific attributes of new sites.

1(1 I•111 a I= =I On MO MI MN I= NM MN MIS

231 22- 20 23 E a I yl 10; 10 1 1°01 0 o c,, Tr 0 c., .1 0 N V' 0

31 36 a. al

al at: 231 g. P 5 id 10 101 10

0 0 0 N vt 0 CV .1 itt •ct 0

31 30 21 20 101 10 01 0 0 o N Log abundance

Baendae Heptagentidae Leptophlebndae Ephemendae Ephemerellidae Caenidae

Fig 2.3. The log category abundance data for each mayfly family at 42 chalk stream sites in spring, summer and autumn. The '0' log abundance category (unshaded) indicates the number of sites at which the family was absent in a given season. Log category 1 = <10 individuals per sample; 2 = <100; 3 = < 1,000; 4 = <10,000. IMMEM OM MI - 01= I= NM MN a NM OM a a a a a IM

r%1 - 3. NOTES ON THE LIFE CYCLES OF EACH SPECIES

Despite the fact that a very substantial number of studies have been conducted on the life cycles of mayflies in Europe, our knowledge is far from complete This is, in part, due to the fact that in some mayflies the life cycle shows flexibility, depending on the environmental conditions. In addition, where a species is capable of having several generations in a year, interpretation of the life cycle can be problematic when based on field observations alone. Hence, many workers in this field emphasize the importance of both field and laboratory studies (egg hatching and larval growth) for the correct interpretation of the life cycles (Brittain, 1982, Elliott et al. 1988)

Elliott and Humpesch (1983) and Elliott el a/. (1988) have collated the extensive European literature on the flight periods and life cycles of mayflies found in Britain. Information from these two publications is reproduced in Table 3.1 for the 26 taxa being considered in this report. Note that the flight periods include observations from many varied streams and rivers within Europe and so, flight periods in southern chalk streams may be more restricted in some cases. An example is Ephemera danica, which is normally observed in May/June, although emergence at other times of the year is not unknown.

Elliott et a/. (1988) classify the life cycles of the British species into five broad categories, which are listed and defined in a footnote to Table 3.1. Groups IA and 1B are both univoltine (one generation per year) but whereas IA ovenvinters in the egg stage, IB overwinters in the larval stage. Groups 2A and 2B are bivoltine (two generations) or multivoltine (more than two generations per year) but again, 2A overwinters in the egg and 213overwinters in the larval stage. Finally, group 3 has one generation every two years (every three years in some northern latitudes). Note that more than one category is offered for some species (where life cycle varies with river type or geographical location) and that a question mark is used where uncertainty remains.

The final column in Table 3.1 is reserved for additional notes on some species whose flight periods/life cycles have been studied in southern chalk streams.

The Baetidae in particular, display a considerable degree of life cycle flexibility throughout their distributional range (Brittain, 1982). For example, Haetis rhodani may have a single overwintering generation in northern Europe and in mountainous areas further south. However, a winter generation followed by a summer generation is typical of less extreme conditions and in more southerly locations there may be additional summer generations. Elliott et al (1988) point out that the combination of the long flight period, the long period when eggs are present and the multivoltine life cycle arc the major factors which enable this species to dominate the mayfly fauna of most streams and rivers in Britain

Table 3.1 indicates that all members of the Bactidae are capable of having two or more generations per year (Groups 2A & 2B). Clearly, those with overwintering larvae

II

(Group 213) will have greater capacity for early spring emergence than those which overwinter in the egg stage (Group 2A). Note that B.vernus & B. scamhus group,

Table 31 Information on the flight periods and life cycles of mayflies abstracted from Elliott and Humpesch, (1983) and Elliott el at (1988) respectively, together with additional observations made in southern chalk streams.

Notes Species Flight Period Life Cycle

Baetis atrebatinus may - Oct 213(9) Baetis buceratus Apr - Oct 2B (The(is digitatus May - Scp Baetis mutacus Apr - Oct 28 Baetis niger Apr - Oct 28 Multivoltine (Welton et at 1982) Baths rhodans Jan - Dec 28 Pre-ernergent larvae Mar - Dec' Pre-emergent larvae April -Dec' Baetts vernus Apr - Oct 1A/2A Baths scambus group Feb - Nov 1A/2A Pre-emergent larvae May - Dec' Centropttlum Iuteolum Apr - Nov 28 2 or possibly 3 generations (Welton et at 1982)

Centroptilum pennulatunt May - Oct 2A(?) Cloeon dtptertan May - Oct 28 Procloeon bifidum Apr - Oct 2A(?)

Rhithrogena sp. Mar - Sep I B Ileptagenta sulphurea May - Oct I B Ecdyonurus sp. Mar - Oct I B

Leptophlebia vespertina Apr - Aug 1B Paratcptophlebia cincta May - Aug IANIB(?) et at 1982) Paraleptophlebia submarginata Apr - Jul IB Univoltine (Welton Paraleptophlebia werneri May - Jun I A(?) Univoltine in Winterbournes Habrophlebta fusca May - Sep 1B

Ephemera danica Apr - Nov I B/3 Semivoltine (Wright et al. 1981)

Apr - Nov' Ephemerella ignita Apr - Sept I A/ I B/2B Pre-emergent larvae See also Bass (1976) & Welton et at (1982)

Brachycercus harrisella - July -7 1A(7) Caenis horaria May - Sep I B/2B Caenis rivulorum Apr - Sep I B Univoltinc (Welton et at 1982) Pre-emergent larvae May -June' Caenis luctuosa group May - Sep IB/2B

Group IA. Univoltine (onc generation per ycar), ovenvintering in egg stage. Group 1B. Univoltine, overwintering in larval stage. Group 2k Bivoltine (two generations per year) or multivollinc (more than two generations per year), overwintcring in egg stage. Group 2B. Bivoltinc or multivoltine, overwintering in larval stage. Group 3. Sentivoltine (one generation every two years or even every three years).

Data on the occurrence of pre-emergent larvae taken front University of Reading (1978)

14 which have overwintering eggs, (and also C pennulantm & Procloeon hifidum which are believed to have overwintering eggs), are less frequently encountered in spring samples in relation to those collected in summer and autumn (see Table 2.2).

Welton et at(1982) studied the growth and production of five species of mayflies in a recirculating fed by borehole water whose chemistry was similar to local chalk streams in Dorset. The most abundant species was B.rhodani, and they were able to recognise five cohorts through the year. Their study also included C. luteolum, which had two and possibly three cohorts per year. In a separate study conducted at seven chalk stream sites during the mid-1970's (University of Reading, 1978) 5-minute pond-net samples were collected each week and pre-emergent larvae (with darkened wing-buds) were removed to document emergence patterns and attempt to recognise discrete generations. Pre-emergent larvae belonging to B.rhodani, B.vernus and B.scambus group began to appear at various times in spring (Table 3.1) and were sometimes recorded into December. In all cases there was convincing evidence of at least two generations.

In general, those Heptageniidac and Leptophlebiidae represented in Table 3.1 appear to have simple univoltine life cycles with overwintering larvae in most cases. However Paraleptophlehia werneri, which is believed to overwinter in the egg stage, must adopt this strategy in winterbourne streams, which dry out in summer leaving the resistant eggs within the stream bed. After the springs break in winter, the eggs can then hatch in early spring and rapid larval growth allows emergence to take place before the stream dries out once more.

In southern chalk streams, Ephemera danica has been shown to have a two year life cycle (Wright et at 1981), with emergence in late May/ early June

Whereas Ephemerella ignita is univoltine with overwintering eggs in many streams in Britain, larvae occur throughout the year in southern chalk streams (Bass, 1976). University of Reading (1978) recorded pre-emergent larvae from April to November and Kite (1962) observed adults on the wing in all months of the year in southern England. The reason for these differences is related to egg hatching. Elliott et at (1988) demonstrated that in cool streams, a small proportion of eggs do hatch through the autumn and winter, but the main egg hatching period is between March and May, resulting in emergence between April and September. Chalk streams remain relatively warm through' the autumn and winter months, allowing a higher percentage of eggs to hatch. Nevertheless, the highest densities of larvae recorded in small chalk streams were in April (Welton et a/. 1982) or May (Bass 1976) and the peak densities of pre- emergent larvae in the seven chalk streams examined by University of Reading (1978) were observed between May and July.

Information is limited for the Caenidac. The single generation of Caents rivulorum studied in the recirculating channel (Welton et at 1982) started to emerge in May, and University of Reading (1978) only recorded pre-emergent nymphs in May and June. The seasonal occurrence of C. luctuosa group (Table 2 2) in which specimens were recorded at most sites in summer suggests somewhat later emergence than C. rivulorum

15 MO MENNIO a a Ma MIMIMSIMMIMIMMIMEMMOIM 4. FACTORS AFFECTING THE DISTRIBUTION AND ABUNDANCE OF EPIIEMEROPTERA

4.1. Habitats, habits and feeding behaviour of the larvae

Elliott el al. (1988) provide a summary of the habitats, habits and feeding behaviour of the British Ephemeroptera. More recently, Wright el at (1993) undertook a survey of macroinvertebrate-habitat associations at 76 lowland running-water sites in England and Wales A large number of different habitats were sampled within three broad categories. non-macrophyte, submerged macrophyte and emergent macrophyte. Early analyses, based on these categories and using mayflies at family level only, demonstrated statistically significant positive associations between submerged macrophytes (Baetidae & Ephemerellidae), emergent macrophytes (Leptophlebiidae), non-macrophytes (Eleptageniidae & Ephemeridae) and no significant associations for Caenidae (Wright ci al 1994). The habitat preferences of the individual species of mayflies in this study (Wright et al. 1993) are given in italics in Table 4.1. All other details on habit and feeding behaviour are taken directly from Elliott ei at (1988).

The descriptions of 'habit' need brief explanation. 'Swimmers', including many Baetidae, have a torpedo-shaped body whereas 'clingers' (e.g Heptageniidae) are dorso-ventrally flattened and have large curved tarsal claws. Sprawlers (e.g Caenidae) are poor swimmers and live in the surface layers of fine or on the surface of macrophytes. 'Climbers' (eg Centropnlum spp ) are adapted to life amongst the stems of macrophytes whilst burrowers such as Paraleplophlebia spp. and Ephemera danica live in river Larvae of all thc British species of mayflies are herbivores and feed on detritus or periphyton (algae and associated material on macrophytes and non-macrophyte substrata). 'Scrapers' exploit periphyton, 'collector gatherers' eat fine deposited detritus, whilst 'collector filterers' feed on fine detritus in suspension Note that the diet of larvae is not fixed but may vary with the stage of development, time of year and the habitat/river in which the species occurs. Further information on both habits and feeding types may be found in Elliott et at 1988.

Table 4.1 Running-water habitats (from Wright et at 1993), together with habits and feeding behaviour (from Elliott et aL 1988) for thc mayflies found in southern chalk streams. See text for further explanation

Species Running water habitat Habit Feeding Behaviour

Baetis atrebatinus Submerged & emergent Swimmer Scraper & collector- gatherer macrophytes

Baths bucernms Submerged macrophoes Swimmer Scraper & collector- gatherer

Baths digitatus Submerged macrophytes Swinuned climber Scraper & collector- gatherer

Baths muncus Submerged & emergent Burrower Scraper-gathererAscraper") macrophytes

Lketis niger Submetxed & emergenl Swimmer/climber Scraper and -gatherer macrophprs

17

Scr aper and collector Baths rl«xlani Submerged & emergent Swimmer - gather er macrophytes plus non. macrophytes

Scraper and collector-gatherer Baths vemus Submetged & emergent Swimmer macrophytes

Scraper and collector-gatherer Baths scambus group Submerged & emergent Swimmer/Climber macrophytes

Collector-gatherer Centroptilum luteolum Emergent macrophytes Swimmer/Climber

Swimmer/Climber Collector-gatherer Centroptilum pennulatum Emergent macrophytes

Swimmer/CI imber Collector-gatherer Cloeon dipterion Emergent macrophyles

Swimmer/CI imber Collector-gatherer Procloeon bifidum Emergent & submerged macrophytes plus non- macrophytes

Clinger Scraper and collector-gatherer Rhithrogena sp Non-macrophytes

Clinger & swimmer Scraper and collector-gatherer Heptagenia sulphurea Submerged macrophytes

Clinger & swimmer Scraper and collector-gatherer Ecdyonunts sp. Non-macrophytes

Sprawler & climber Collector-gatherer Leptophlebia vespernna Running water (pools/margins and on macrOphytes)

Burrower Collector-gatherer Pamleptophlebia moo Submerged & emergent macrophytes

Burrower Collector-gatherer Paraleptophlebia submarginata Submerged macrophytes

Burrower Collector-gatherer Paraleptophlebta wernen Emergent macrophytes

Sprawler & climber Collector-gatherer Habrophlebia fusca Emergent & submerged macrophytes plus non- macrophytes

Burrower Collector-filterer Ephemera danica Non-macrophytes plus submerged &emergent macrophytes

Ephemerella ignita Submerged macruphytes Clinger & sprawler Collector-gatherer

13mchycercus hamsella Submerged & emergent Sprawler Collector-gatherer macrophytes plus non- macrophytes

Caenis hararia Emergent macrophytes Sprawler Collector-gatherer

Caenis r•vulantm Non-macrophytes plus Sprawler Col lector-gatherer submerged & emergent macrophytes

Caenis luctuoso group Non-macrophytes plus Sprawler Collector-gatherer emergent & submerged macrophytes

I S 4.2. The impact of discharge regime

From the previous section it is apparent that the many species of mayfly larvae found in southern chalk streams exploit a wide range of habitats and rely on different food sources. Chalk streams exhibit a number of characteristic features which are critical to the maintenance of the habitats and food resources used by the entire macroinvertebrate fauna, including the mayflies. These features are well documented (Berrie 1992) and include.

I). The relatively stable flow regime within the perennial section, with peak flows in late winter followed by a falling through the summer and autumn. The seasonal nature of the flow regime in the winterbourne section above the perennial head, where flow is dependant upon replenishment of the chalk in winter. The appearance of water from the chalk aquifer at a temperature of —I 1°C throughout the year, resulting in chalk streams being warm in winter and cool in summer relative to streams which lack a groundwater component. 4) The presence of crystal-clear water with a high calcium content, due to the slow filtration of the rain water through the cracks and fissures in the chalk.

These varied features allow the development and maintenance of the submerged and emergent macrophytes which contribute to the wide diversity of habitats found within chalk streams. They also provide an enormous surface area on which algae can grow and within which both fine and coarse organic matter, including autumn-shed tree leaves, can be trapped. In this way, chalk streams normally maintain varied habitats and food resources year-round, resulting in both species-rich assemblages and high densities of individuals.

Some variation in the flow regime can be expected from year to year, and the fauna is adapted to tolerate a range of conditions. Chalk streams, by their very nature, are not prone to events, and the pattern of discharge most likely to cause concern is a low flow regime. Low flows can be the result of natural droughts and/or man-made abstraction. The impact of a natural drought on a chalk stream ecosystem will depend upon many factors, including thc length and severity of the drought and also the season in which it starts and ends. Similarly, the ecological effects of abstraction will depend on the extent to which the natural hydrograph is modified and whether the river is already experiencing a natural drought.

In view of the fact that the different species of mayfly found in chalk steams are adapted to a variety of habitats and exploit different food resources, they can be expected to give different responses to low flow conditions These may be direct responses to changes in the physical environment (e.g. velocity, temperature regime or siltation) or indirect responses mediated through changes in the available habitat or food resources.

Studies in both N.America and Europe have noted an increase in invertebrate drift in response to conditions of low discharge, low current velocity and increased sediment loading (Brittain 1982, Brittain & Eikeland 1988, Elliott et al. 1988) In particular,

19 Corrarino & 13runsven (1983) observed catastrophic drift in &ens (and Sttnuburn) in experimental channels subjected to reduced stream discharge, whilst Zelinka (1984) demonstrated that low discharge, which gave rise to low current speeds and siltation, led to loss of mayfly populations in experimental brooks.

The impact of low flows on the macrophytes and other habitats in chalk stream has been documented in a number of studies. In the 1970's, long-term studies of the aquatic macrophytes of shaded (Ham et al 1982) and unshaded sites (Ham et al 1981) in the lower perennial of the R.Lambourn included both minor (1973) and major (1976) drought events. Another unshaded site in the upper perennial of the R.Lambourn was monitored during the 1976 drought, as were three more sites on the R.Kennet (Wright & Berrie 1987). Growth of Ranunculus, an important habitat for many species of mayfly larvae, was poor during the drought of 1976, and was frequently accompanied by siltation of the river bed. Such major changes in the availability of the dominant habitats and their contained food resources would be expected to have significance for all macroinvertebrates, including mayfly larvae.

Ladle & Bass (1981) examine the flora and fauna of a small chalk stream in Dorset between 1973 & 1974, and during their study the 1973 drought transformed an essentially perennial discharge regime into an intermittent one between September and December 1993, with striking consequences. Following the return of water in 1974, the density of Ephemerella ignita reached over 9,000 ni2 in May, compared to a little over 2,000 M2 the previous May.

More recently, Wood & Petts (1994) studied a small chalk stream, the Little Stour, in Kent They monitored the ecological effects of a protracted drought, exacerbated by groundwater abstraction, and the subsequent partial recovery of the stream in 1993. In both 1992 and 1993 just six species of mayfly larvae occurred, but whereas in 1992 Baetis rhodani was scarce on just three sites, in 1993 higher numbers were recorded at eight study sites.

The detailed studies undertaken on the R.Lambourn in the 1970's (Wright 1992, Wright & Symes in press) are crucial to an understanding of the impact of the discharge regime on mayfly larvae. Only through long-term studies which include years of high and low discharge will patterns emerge which provide reliable data. Between 1971 & 1979 quantitative samples were taken on each of five habitats (Gravel, Ranunculus, Benda, Callitriche and silt) and on- each of two sites (shaded and unshaded) in June and December each year. In each month, data were also available on the area. of stream bed occupied by each major habitat. Wright and Symes (in press) present data for the shaded site in which the densities of a number of important families of macroinvertebrates are weighted according to their density on each habitat and also the area of each habitat on the river bed This provides the best overall estimate of density for the site, given the complexity of habitats present.

The main findings for the three families of mayflies of greatest interest to fishermen (Baetidae, Ephemerellidae and Ephemeridae) are as follows:

Baetidae - (—six species) In drought years (1973 & 1976) weighted mean densities of larvae in June were low (— 500 mi compared to some years with high discharge

20 (1975 & 1977) where densities were around 5,000 rn'' Most other years had intermediate densities, although 1979 was rather low for the discharge regime as a result of the restrictcd arca of macrophyte. In 1992, densities were abnormally low, as a consequence of hatch repairs during the spring which disrupted the normal pattern of flow through the study site.

Ephemerellidac (i.e. Ephemerella ignita) - densities of larvae could not be related to the discharge regime and in June, rarely exceeded —2,500 ni2. However, in the year following a drought, higher densities were found with —4,000 R1-2 in 1974 and —9,000 111-2in 1977.

Ephemeridae (i.e. Ephemera clanica) - densities of larvae were at a high level at the outset of the study, but following emergence in late May 1972, larval densities were very low in December 1972, suggesting poor recruitment as a result of the cool damp conditions during the period of flight activity. The recruitment observed in subsequent generations (December 1974, 1976 & 1978) was progressively higher in each generation, suggesting that the discharge regime was not the most critical factor in this semivoltine species (See Wright et al. 1981 and also section 4.4. for further details)

(Note- In 1997, the Environment Agency commissioned further studies on the macrophytes and macroinvertebrates of sites on the R Lambourn and R.Kennet first examined during the 1970's (R.Lambourn at Bagnor and the R.Kennet at Littlecote and at Savernake).The sampling regime for June and December 1997 was identical to that used in the 1970's and should provide further information of relevance to .an understanding of the response of the fauna to the recent prolonged drought).

4.3. The impact of pollution

Mayfly larvae have been used as indicators of water quality, because of their widespread occurrence, importance in aquatic food webs and sensitivity to a wide range of pollutants. For example, they have been used in the detection of organic pollution, heavy metals, detergents, pesticides, petroleum products, pulp mill effluent and the effects of acidification (Brittain 1982) Fortunately, many of these problems are irrelevant or of relatively minor concern when considering the case of chalk streams. Early recognition of the importance of game fisheries on chalk streams and sustained interest and vigilance to ensure that these unique systems are not compromised has helped to minimize point source pollution inputs. However, in this heavily populated country, there will inevitably be cases of organic pollution on some chalk streams, whether through sewage effluent, fish farm effluent or farm wastes.

The BMWP score system (National Water Council, 1981) gives scores to families of macroinvertebrates (including the six mayfly families considered in this report) such that a high score represents intolerance to organic pollution and a low score represents increasing tolerance (score range is 10- I).

21 The relevant scores are as follows,

10 - Ephemerellidae 10 - Leptophlebiidae 10 - Ephemeridae 7 - Caenidae 10 - Heptageniidae 4 - Baetidae

Thus, in the BMWP system, most families of mayflies are regarded as very pollution intolerant, and only the Caenidac and more particularly the Baetidae have some tolerance to organic pollution. Within the Baetidae, Baetis rhodani has normally been regarded as the most pollution tolerant species (Woodiwiss, 1964).

Hellawell (1986) also provides information on the pollution tolerances of common European macroinvertebrates, derived largely from their position in published tables based on the 'Saprobien system'. Interestingly, the position of some of the individual species of relevance to this study does not link directly to the cruder BMWP categories given above. Thus:

Species largely intolerant of organic pollution (oligosaprobic) Ecdyonurus sp Rhithrogena sp. Paraleptophlebia submarginata

Species tolerant of moderate organic enrichment (beta - mesosaprobic) Baetis rhodani Brachycercus harrisella Caenis luctuosa Cloeon diptentm Ephemera danica Ephemerella ignita Heptagenia sulphurea

Species tolerant of severe organic pollution (alpha - mesosaprobic) Baetis vernus Caetzis horaria

Pinder & Farr (1987) examined a number of sites on the R.Frome in Dorset at which there was visible evidence of organic pollution by sewage, fish farm effluent and farm waste. In practice, the low levels of organic enrichment they encountered did not have an adverse effect on faunal associations within the river and diversity indices were positively correlated with dissolved organic carbon.

In a recent study by Quinn & Hickey (1993), the response of benthic invertebrates to domestic sewage waste stabilization lagoon effluent was examined by sampling upstream & downstream of the discharges in eight streams in New Zealand. Whereas at low organic solids loadings the densities of Ephemeroptera, Plecoptera and Trichoptera increased by up to 50%, at higher loadings there was more than a 50% reduction in the densities of sensitive taxa in these three groups. In addition, trout farm effluent has been shown to decrease the taxon richness of Ephemeroptera, Plecoptera

22 and Trichoptcra below and tor at least I 5 km downstream of the outfall from three commercial trout farms in North America (Loch, West & Perlmutter 1996)

In cases where organic pollution leads to the elimination of BMWP families, biologists within the Environment Agency are familiar with standard techniques based on RIVPACS (Wright 1995, Murray-Bligh et at 1997) which use observed/expected ratios for the number of BMWP taxa and Average Score Per Taxon (ASPT) for the detection of environmental stress. Finally, it is important to bear in mind that the impact of pollution may be exacerbated under conditions of low flow.

4.4. Factors affecting the terrestrial (adult) phase

Mayflies represent the oldest of the existing winged and are unique in possessing two winged adult stages, the subimago and the imago (commonly referred to as 'duns' and 'spinners' by fishermen) The adult stages do not feed, and therefore depend upon energy reserves acquired by the larvae. In some species, adults only live for 1-2 hours, in others the life span is from a few days to a maximum of two weeks. Mating takes place during aerial flight, but the dispersive potential of mayflies is only moderate (Brittain 1982, 1990). Thus, only a small fraction of the life span is spent as the adult, but nevertheless, this stage is crucial for successful reproduction and dispersal.

Elliott and Humpesch (1983) provide a detailed account of the adult phase under the following three headings: 1).Emergence and flight period. 2). Flight behaviour and mating. 3) Fecundity and oviposition behaviour, including egg development. Their review collates data on the behaviour and ecology of many of the species occurring in chalk streams and includes information on emergence behaviour and timing, factors affecting emergence, time when males swarm, fecundity of the different species and oviposition behaviour. In view of the detailed information readily available in this publication, it will not be repeated here. It is, however, worth mentioning that different authors, working on the same species, often disagree on the time of day at which emergence takes place, probably because variations in the diel cycle of water temperature and light intensity affect emergence (Elliot and Humpesch 1983).

Given that the characteristic behaviour and ecology of the pre-emergent larvae and the adults of each species has evolved to maximize the chance that females will be successful in laying eggs to ensure the next generation, what is known of factors which may cause significant disruption to this phase of the life cycle? The answer would appear to be very little. The larval stage occupies a high proportion of the life span and much attention has focused on factors affecting the distribution and abundance of larvae. In contrast, the assumption is normally made that if sufficient larvae reach the adult stage, then the high fecundity of most species will ensure thc next generation. In the vast majority of cases this must be true, but not before the pre-emergent nymphs and adults have survived a number of obstacles. At emergence, the mature is particularly vulnerable to predation by fish The response of trout to the emergence of Ephenwra danica is well recorded by fishermen. After emergence, the subimago

21 normally flies away from thc river to shelter amongst vegetation where it moults to the imago. Swarming (limited to males except in the Caenidae) often occurs in relation to bushes or trees near water and females then fly into the male swarm in order to mate. During the life of both subimago and imago, further predation by dragonflies, birds and even bats may influence the numbers of females able to return to water to lay their eggs. Apparently, a number of different parasites of mayflies exploit these food chain links in order to complete their own life cycles (Brittain 1982).

Despite the need to minimize losses due to predation and parasitism and find suitable habitat for shelter and terrain markers for swarming, the terrestrial phase is normally effective at performing its essential role. However, inclement weather in the form of low temperatures, high winds and rain may have the potential to disrupt mating swarms and subsequent oviposition. This view has often been taken by fishermen (Macan 1969, and references in Wright et at 1981) and now, circumstantial evidence based on larval populations is available to support this viewpoint (Wright el al. 1981). On four sampling occasions in 1971, the weighted mean density of Ephemera danica on the R. Lambourn at Bagnor (shaded site) was around 500 ni2 (Wright & Symes in press), but following cold damp weather during the period of flight activity in May/June 1972, the densities of larvae recorded in December 1972 were very low (-- 27 ni2). Recovery to high densities took several generations and weighted mean densities for December 1974, 1976 and 1978 were estimated at —71, —142 and 2,300 rn'2. Whelan (1980) also records that in 1972, gale force winds drowned large numbers of emerging E.danica on lakes in Ireland, and prevented those that survived from making their egg-laying flight to the lake margin.

24 5. REFERENCES

I3ass, 1.A.B. 1976. Studies on kphemerella igthta (Poda) in a chalk stream in southern England. Hydrobiologia 49, (2), 117-121.

Berrie, A.D. 1992. The chalk-stream environment. Hydrobiologia 248, 3-9.

Blackburn, J.H., Gunn, R.J.M. & Hammett, M.J. (in press). Electrogena affinis (Eaton, 1885) (Ephemeroptera, Heptageniidae), a mayfly new to Britain. Entomologist'sMonthly Magazine.

Bratton, J. H. 1990. A review of the scarcer Ephemeroptera and Plecoptera of Great Britain. Research and Survey in Nature Conservation, No 29, Nature Conservancy Council, Peterborough.

Brittain, J.E. 1982. Biology of mayflies. Annual Review of Entomology 27, 119-147.

Brittain, J.E. 1990. Life history strategies in Ephemeroptera and Plecoptera. In: Mayflies and Stoneflies. (Ed. I.C. Campbell). 1-12. Kluwer Academic Publishers, Dordrecht, Netherlands.

Brittain, J.E. & Eikeland, T.J. 1988 Invertebrate drill - A review. Hydrobiologia 166, 77-93.

Corrarino, C.A. & Brusven, M A 1983. The effects of reduced stream discharge on insect drift and stranding of near shore insects. Freshwater Invertebrate Biology, 2, 88-98.

Elliott, J.M. & Humpesch, U.H. 1983. A key to the adults of the British Ephemeroptera with notes on their ecology. Scientific Publications of the Freshwater Biological AssociationNo. 47, 10Ipp.

Elliott, J.M., Humpesch, U.H. & Macan, T.T. 1988. Larvae of the British Ephemeroptera: A key with ecological notes. Scientific Publicationc of the Freshwater Biological AssociationNo. 49, 145pp.

Gunn, R.J.M. & Blackburn, J.H. 1997. Caenis pseudorivulorum Kieffermiiller (Ephemeroptera, Caenidae), a mayfly new to Britain. Entomologist'sMonthly Magazine 133, 97-100.

Gunn, R.J.M, & Blackburn, J.H. (in press). Caenis beskidensis Sowa (Ephemeroptera, Caenidae), a mayfly new to Britain. EntomologistisMonthly Magazine.

Ham, S.F., Wright, J.F. & Berrie, A.D. 1981. Growth and recession of aquatic macrophytes on an unshaded site of the River Lambourn, England from 1971 to 1976 Freshwater Biology, L I, 381-390

25 Ham, S.F , Cooling, D.A., Hiley, P.D., McLeish, P.R., Scorgie, H.R.A. & Bethe, A.D. 1982. Growth and recession of aquatic macrophytes on a shaded section of the River Lambourn, England, from 1971 to 1980 Fresinvater Biology, 12, 1-15.

Hellawell, J.M. 1986 Biological indicators of freshwater pollution and environmental management. Elsevier Applied Science, London & New York. 546pp.

Kite, 0.W. A. 1962. Notes on the emergence of ephemeropteran subimagines in 1961. Salmon & Trout Magazine 165, 124-131.

Ladle, M. & Bass, J.A.B. 1981. The ecology of a small chalk stream and its responses to drying during drought conditions. Archni far Hydrobiologie 90, (4), 448-466

Loch, D.D, West, J.L.& Perlmutter, D G. 1996. The effect of trout farm effluent on the taxa richness of benthic macroinvertebrates. Aquaculture 147, (1-2), 37-55.

Macan, T.T. 1969. The study of mayflies (Ephemeroptera). Bulletin of the Amateur Entomologists Society No.283 16pp.

Murray-Bligh, J.A.D., Furse, M.T , Jones, F.H., Gunn, R.J.M., Dines, R.A.& Wright, H. 1997. Procedure for collecting and analysing macroinvertebrate samples for RIVPACS. Environment Agency & Institute of Freshwater Ecology.

National Water Council 1981. River quality: The 1980 survey and future outlook. National Water Council, London. 39pp.

Pinder, L.C.V. & Farr, I.S. 1987. Biological surveillance of water quality - 3. The influence of organic enrichment on the macroinvertebrate fauna of small chalk streams. Archiv fik Hydrolnologie 109, (4), 619-637

Quinn, J.M. & Hickey, C.W. 1993. Effects of sewage waste stabilization lagoon effluent on stream invertebrates. Journal of Aquatic Ecosystems and Health 2, (3), 205-219.

University of Reading. 1978. Ecological study of chalk streams. Report for the period October 1973 to September 1977. A report by the University of Reading to Thames Water Authority and Central Water Planning Unit. 203pp.

Welton, J.S., Ladle, M & Bass, J.A.B. 1982. Growth and production of five species of Ephemeroptera larvae from an experimental recirculating stream. Freshwater Biology, 12, 103-122.

Whelan, K.F. 1980. Some aspects of the biology of Ephemera danica Mull. ((Ephemeridae, Ephemeroptera) in Irish waters. In: Advances in Ephemeroptera Biology. (Eds F. Flannagan & K.F. Marshall)..187-199. Plenum Press, New York.

26 Wood, P.J. & Pens, G E 1994 Low flows and recovery of macroinvenebrates in a small regulated chalk stream. Regulated Rivers: Research and Management, 9, 303- 316.

Woodiwiss, F.S. 1964. The biological system of stream classification used by the Trent River Board. Chemistry and Industry, 11, 443-447.

Wright, J.F. 1992. Spatial and temporal occurrence of invertebrates in a chalk stream, Berkshire, England. Hydrobiologia 248, 11-30.

Wright, J.F. 1995. Development and use of a system for predicting the macroinvertebrate fauna in flowing waters Australian Journal of Ecoloa 20, 181- 197.

Wright, J.F. & Berrie, A D. 1987. Ecological effects of groundwater pumping and a natural drought on the upper reaches of a chalk stream. Regulated. Rivers: Research and Management 1, 145-160

Wright, J.F., Welton, IS., Furse, M.T. & Gunn, R.J.M. 1988. The macroinvertebrate fauna of the Moors River and Uddens water in Dorset. Proceedings of the Dorset Natural History and Archaeological Society, 110, 127-35.

Wright J.F., Clarke, R.T. & Blackburn, LH. 1993. Macroinvertebrates in lowland rivers in summer. A guide to macroinvertebrate-habitat associations. Report to Scottish Natural Heritage, 107pp

Wright, J.F., Blackburn, J.H., Clarke, R.T. & Furse, M.T. 1994. Macroinvertebrate- habitat associations in lowland rivers and their relevance to conservation.

Verhandlungen Internationale Vereinigung Limnologie 25, 1515- 1518.

Wright, J.F., Hiley, P.D. & Berrie, A D 1981. A nine-year study of the life cycle of Ephemera danica Mull. (Ephemeridae.Ephemeroptera) in the River Lambourn. Ecological Entomolology 6, 321-331.

Wright, J.F. & Symes, K.L. (in press). A nine-year study of the macroinvertebrate faunaof a chalk stream Hydrological Processes.

Zelinka,M. 1984. The effect of low discharge rates on mayflyfauna. In: Proceedings of the 4thInternational conference on Ephemeroptera. (Eds V. Landa et al) CSAV, 323-328.

27 MI SIM INNIINIMIONNO IINIMEMMINIMONNIMIIMMI MN Appendix I. Specification for the scientific review of the mayfly fauna of southern chalkstreams

Background

Staff at the River Laboratory have access to a wide range of published and unpublished information on the Ephemeroptera (mayflies) of chalk streams. The available sources of information include:

The RIVPACS III data-base, which has species-level data for many chalk stream sites in southern England.

Lambourn Project data, including a run of 9 years daia (1971-79) on the macroinvertebrate fauna of two study sites on the R.Lambourn. (This includes the drought year of 1976). Information is also available on the occurrence of pre-emergent mayfly nymphs at 11 chalk stream sites in southern England over a period of 1 or, at some sites, 2 years in the mid-1970's. c) Information on the occurrence of mayfly nymphs on different habitat types in lowland streams, including some chalk stream sites. d). Scientific papers on the ecology of mayflies in chalk streams. These include papers written by River Laboratory staff on the , distribution, abundance, life cycles and production of mayflies and their response to adverse environmental conditions such as low flows.

The review will refer to southern chalk streams in general and include the following:

List of mayflies which are characteristic of southern chalkstreams. Overall frequency of occurrence of each species at chalk stream sites of high biological quality (from the RIVPACS III data-set). Variation in the number of species recorded at chalk stream sites in the RIVPACS III data-set. Occurrence of species by season (using gross categories of spring, summer and autumn) and in relation to location along the watercourse. Family level data with attached log categories of abundance based RIVPACS samples in spring, summer and autumn for chalk stream sites (from the RIVPACS data-set). A brief statement on the life cycle of each species.

The above information should provide an indication of the range of species which may be expected at a given chalk stream site in the absence of environmental stress.

The report will also include a thorough review of the factors, both natural and resulting from man's activities, which may have deleterious effects on the distribution and abundance of mayflies.

29 Appendix 2. The 42 southern chalk stream sites from which RIVPACS samples have been obtained.

River EA Region Site NGR Allen South-West Watford Mill SU 010 006 Avon South-West Breamorc SU 163 174 Avon South-West Bulford SU 163 437 Avon South-West Christchurch SZ 158 933 Avon South-West Moortown SU 149 035 Avon South-West Patncy SU 071 585 Avon South-West Rushall SU 132 558 Avon South-West Stratford-Sub-Castle SU 129 330 Bcrc Stream South-West Middle Belt SY 858 923 Candover Southern Abbotstone SU 565 345 Chess Thamcs u/s R. CoInc TQ 066 947 Ed South-West Pains Moor SU 074 105 Ed South-West Upper Farm SU 067 112 Fromc South-Wcst Chantmarle ST 589 023 Frome South-West East Stoke SY 866 867 Frame South-West Frampton SY 623 949 Frome South-West Lower Bockham ton SY 721 904 Frorne South-West Moreton SY 806 895 lichen Southern ChiIland SU 523 325 Itchen Southern d/s Chickenhall SDW SU 466 175 lichen Southern Itchen St.Cross SU 481 282 Itchen Southern Otterbourne Water Works SU 470 233 Kennet Thames u/s Aldershot Water SU 544 659 Lambourn Thames Bagnor SU 453 691 Mimram Thames Codicote Bottom TL 208 180 Mimram Thames Panshanger TL 282 134 Moors/Crane South-West d/s Cranborne SU 062 129 Moors/Crane South-West East Moors Farm SU 101 029 Moors/Crane South-West Great Rhymes Copse SU 077 121 Moors/Crane South-West King's Farm SU 105 064 Moors/Crane South-West Pinnocks Moor SU 077 112 Moors/Crane South-West Redmans Hill SU 074 079 Moors/Crane South-West Romford Bridge SU 075 094 Moors/Crane South-West Vcrwood SU 088 075 Piddle South-West Brockhill Bridge SY 839 928 Piddle South-West Druce SY 744 951 Piddle South-West ST 703 010 Piddle South-West Warcham SY 919 876 Test Southern Lower Brook SU 338 276 Test Southern Romsey SU 352 204 Test Southern Skidmore SU 354 178 Wool Stream South-West Wool SY 848 869

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Appendix 3. Mayflies found at each of the 42 chalk stream sites. Data for the three seasons are combined. 1 indicates taxon occurrence in a single season),whereas 2 (or 3) indicates presence in two or three seasons. MNIIMMMININOMMIMMIONINOMIO DISTRIBUTION SHEET To be completed by all Project Leaders completing commissioned research project reports. Please bind a copy of this distribution sheet as the final page in all internal (IFE) copies of the report

1. Title: Scoping Study on the Ephemeroptera of Southern Chalk Streams

Authors:J.F. Wright, J.H. Blackburn, R.J.M. Gunn, K.L. Symes and J.Bowker.

Report ref: RUT13068A7/3

Master copy held by: J.F. Wright (IFE) A. Frake (Environment Agency, South West Region)

Report access code (assign a suitable code from list below): N

2. DISTRIBUTION LIST [A)-G) standard, H) other] No.copies Date

Contract customer: 1 31.03.98

Director IFE 24.04.98

Deputy Director (title page and abstract only)

FBA Library, Windermere 24.04.98

River Laboratory Library 1 24.04.98

Doreen Sturmey (title page only + no.pages for adding to publication list)

Project leader: LP. Wright 3 24.04.98

Other (list below and indicate no. copies in RH column)

J.H. Blackburn 24.04.98 I. R.J.M. Gunn 24 04 98 2. K.L. Symes 24.04.98 3. J. Bowker 24.04.98 4, Total number of copies made I I

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